Standard ball and socket joints usually comprise a housing, a ball socket made of plastic, a lubricant, e.g., grease, a ball pivot and a sealing system, in general, in the form of a sealing bellows.
Under high loads, e.g., a high pressure load on the bearing or at a high operating temperature, a ball socket made of plastic tends to undergo a change in shape due to the creep of the plastic material. The creep process depends not only on the operating temperature and the mechanical load of the ball socket, but is also affected by the wall thickness of the ball socket. In general, the thicker a ball socket, the more probable is a change in shape of the ball socket due to the creep of the plastic material under high load. If the material of the ball socket creeps too intensely, clearance will develop in the ball and socket joint, which is associated with a great increase in the wear of the material on the joint surface. Standard ball and socket joints with all-plastic sockets can therefore be used only at relatively low pressure loads in the area of the joint surface, so-called surface pressures, and at moderate temperatures.
Ball and socket joint systems with very thin plastic ball sockets are therefore preferred for applications in which higher surface pressures and higher operating temperatures are required.
A process for manufacturing a ball and socket joint, according to which the ball head of a ball pivot is coated with a plastic possessing good lubricating properties, and the coated ball surface is subsequently jacketed with a fiber braiding, is therefore proposed in the patent specification DE 41 08 219 C2. The coated and jacketed ball head is then positioned in a housing mold, and the free space between the fiber braiding applied and the housing mold is filled with a two-component plastic such that it embeds in it the fiber braiding lying on the surface of the coated joint ball. The fibers of the fiber braiding must be oriented corresponding to the directions of the principal loads acting on the ball and socket joint, and the manufacture of the fiber jacketing is therefore somewhat complicated.
The process disclosed in the Offenlegungsschrift DE 31 27 710 A1 for manufacturing a ball and socket joint provides, in contrast, for coating the ball head with a lubricant before a lost form made of a synthetic material is applied to the coated ball head. The ball head thus prepared is subsequently positioned in a mold for the joint housing, and the free space between the prepared ball head and the mold is finally filled out with a synthetic material to form the joint housing. The lost form jacketing the lubricant may consist of a plastic, which solidifies in the form of a thin film. According to this process, the processing temperature of the plastic must be below the drop point of the lubricant used, because the inner surface of the ball socket could otherwise adapt itself to concave deviations of the ball head from the spherical shape. High torques of the joint, associated with rapid wear of the joint, would result as a consequence.